Vitamin D - Its Role and Management in the Bariatric Patient

Vitamin D: Its Role and Management in the Bariatric Patient March 2011 Nazy Zarshenas, BSc, MND, APD Ms. Zarshenas is a Senior Clinical Dietician at St. George Private Hospital, St. George Upper GI Unit, Sydney, Australia Bariatric Times. 2011;8(3):22–23 Introduction Research over the past 20 years has associated vitamin D with a wide range of health benefits including prevention of cancer, cardiovascular disease, hypertension, pre-eclampsia (a medical condition in which hypertension arises in pregnancy), diabetes, and metabolic syndrome.[1–3] Adequate vitamin D intake has also been associated with improved immune response, neuropsychological functioning, and physical performance.[1–3] A recent review by the Institute of Medicine (IOM) found that the strongest benefits of vitamin D and calcium are in bone health.[14] Calcium and vitamin D are essential nutrients for promoting bone growth and maintenance.4 Vitamin D’s role is to maintain normal serum calcium concentration in order to preserve the process of bone mineralization. It does this by stimulating calcium and phosphate absorption through the intestine by working in parallel with parathyroid hormone (PTH) to enhance distal tubule calcium reabsorption, and by increasing bone reabsorption. This installment of “Nutritional Considerations in the Bariatric Patient” will discuss the health benefits associated with proper vitamin D intake in the bariatric surgery patient. Screening for and treating vitamin D deficiency Bariatric surgery procedures often result in nutritional deficiencies, with vitamin D being the most common.[5–12] In fact, the prevalence of vitamin D deficiency in the bariatric surgery population has been reported to be as high as 84 percent.[13] To prevent exacerbation of nutritional deficiencies, it is imperative to screen for and treat any deficiencies preoperatively. Vitamin D is a prohormone, as it can be synthesised endogenously. The sources of vitamin D are as follows: 1. Exposure to sunlight. Cholecalciferol (i.e., vitamin D3) is formed in the skin through the action of ultraviolet (UV) light on 7-dehydrocholesterol to produce cholecalciferol. 2. Diet. Ergocalciferol (vitamin D2) is the dietary source of vitamin D. It is found in small quantities in fatty fish (e.g., North Sea salmon, herring, and mackerel), liver, eggs, and fortified foods (e.g., dairy products, cereals). Ergocalciferol is also used as the major source of supplementation.[4] The Dietary Reference Intakes (DRIs) for calcium and vitamin D have recently been updated. The DRIs for calcium and vitamin D for healthy adults are 1,000 to 1,300mg per day and 600IU per day, respectively. A total of 800IU per day of vitamin D has been recommended for individuals above the age of 70, with a general upper (safe) level of 4000 IU.[14] These DRIs are devised for the general public and should not be applied to population groups at high risk of developing vitamin D deficiency, which includes individuals with obesity. Also, patients with medical conditions that predispose them to vitamin D deficiency, such as inflammatory bowel disease, celiac disease, and pancreatic insufficiency are also at higher risk and need close monitoring.[5,15] To diagnose vitamin D deficiency, 25 hydroxy vitamin D (25-OHD), iPTH, calcium, albumin, and creatinine levels should be evaluated.[4,15] There is much debate as to the optimal level of 25-OHD. Some sources consider 20µg/mL to be adequate and other sources suggest >30µg/mL to be the optimal level.[16] Most recently, the IOM has reported that there is not enough evidence to support the benefit of achieving levels 30µg/L.[14] The current recommendations for treating moderate-to-severe vitamin D deficiency in the nonbariatric patient are 3000 to 5000 IU per day for at least 6 to 12 weeks, followed by 1000 IU.[15] The two most common vitamin D preparations are Cholecalciferol (D3) and ergocalciferol (D2). Some studies[23,24,25] have shown that D3 has a greater potency than D2 in treating vitamin D deficiency. However this is not consistent throughout the literature.[26] Furthermore the efficacy of these two preparation needs further investigation in obese patients. One small pilot study[27] comparing the these two forms of vitamin D preparations found a better suppression of PTH with D3 than D2. However, as different doses of the two forms of vitamin D were used we can not draw any direct comparison from this study. Alternatively, a higher dose vitamin D2 50,000 IU once per month for 3 to 6 months may be prescribed (compounded high-dose Vitamin D can be prescribed if high-dose Vitamin D is not available). A 300,000 to 600,000 IU vitamin D3 given intramuscularly, once or twice per year, has also shown to be effective.[17]

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